fix(api): Handle objects without REST serializers (#23363)

The job and tagged item serializers fell back to a nonexistent
object_repr attribute when the related model had no REST API
serializer, so both lists returned HTTP 500. Both object fields now use
GFKSerializerField with allow_missing_serializer and return null, as
change records do. The jobs list now prefetches the objects, so its
query-count baseline drops from 12 to 11.

Fixes #23310

netbox/core/api/serializers_/jobs.py

@@ -1,15 +1,9 @@
-from functools import cached_property
-
-from drf_spectacular.utils import extend_schema_field
-from rest_framework import serializers
-
 from core.choices import *
 from core.models import Job
-from netbox.api.exceptions import SerializerNotFound
 from netbox.api.fields import ChoiceField, ContentTypeField
+from netbox.api.gfk_fields import GFKSerializerField
 from netbox.api.serializers import BaseModelSerializer
 from users.api.serializers_.users import UserSerializer
-from utilities.api import get_serializer_for_model
 
 __all__ = (
     'JobSerializer',
@@ -25,8 +19,10 @@ class JobSerializer(BaseModelSerializer):
     object_type = ContentTypeField(
         read_only=True
     )
-    object = serializers.SerializerMethodField(
-        read_only=True
+    # A plugin model can support jobs without a REST API serializer
+    object = GFKSerializerField(
+        read_only=True,
+        allow_missing_serializer=True
     )
     notifications = ChoiceField(choices=JobNotificationChoices, read_only=True)
 
@@ -38,24 +34,3 @@ class JobSerializer(BaseModelSerializer):
             'queue_name', 'notifications', 'log_entries',
         ]
         brief_fields = ('url', 'created', 'completed', 'user', 'status')
-
-    @cached_property
-    def _object_serializers(self):
-        return {}
-
-    @extend_schema_field(serializers.JSONField(allow_null=True))
-    def get_object(self, obj):
-        """
-        Serialize a nested representation of the object.
-        """
-        if obj.object is None:
-            return None
-        try:
-            serializer_class = get_serializer_for_model(obj.object)
-        except SerializerNotFound:
-            return obj.object_repr
-        if serializer_class not in self._object_serializers:
-            self._object_serializers[serializer_class] = serializer_class(
-                nested=True, context={'request': self.context['request']}
-            )
-        return self._object_serializers[serializer_class].to_representation(obj.object)

netbox/core/tests/query_counts.json

@@ -3,6 +3,6 @@
   "datafile:list_objects_with_permission": 17,
   "datasource:api_list_objects": 12,
   "datasource:list_objects_with_permission": 17,
-  "job:api_list_objects": 12,
+  "job:api_list_objects": 11,
   "job:list_objects_with_permission": 19
 }

netbox/core/tests/test_api.py

@@ -2,7 +2,7 @@ import uuid
 from unittest.mock import patch
 
 from django.contrib.contenttypes.models import ContentType
-from django.test import override_settings
+from django.test import override_settings, tag
 from django.urls import reverse
 from django.utils import timezone
 from django_rq import get_queue
@@ -13,10 +13,11 @@ from rq.job import JobStatus
 from rq.registry import FailedJobRegistry, StartedJobRegistry
 
 from core.api.serializers import DataSourceSerializer
-from dcim.models import Site
+from dcim.choices import PortTypeChoices
+from dcim.models import FrontPort, PortMapping, RearPort, Site
 from users.constants import TOKEN_PREFIX
 from users.models import ObjectPermission, Token
-from utilities.testing import APITestCase, APIViewTestCases, GraphQLQueryTest, TestCase, create_tags
+from utilities.testing import APITestCase, APIViewTestCases, GraphQLQueryTest, TestCase, create_tags, create_test_device
 from utilities.testing.mixins import RQQueueTestMixin
 from utilities.testing.utils import disable_logging
 
@@ -376,6 +377,27 @@ class JobTestCase(
         for obj in objects.values():
             self.assertNotIn('custom_fields', obj)
 
+    @tag('regression')  # Ref: #23310
+    def test_list_objects_without_serializer(self):
+        """Jobs whose object has no REST API serializer, or that have no object, list a null object."""
+        self.add_permissions('core.view_job')
+        device = create_test_device('Device 1')
+        front_port = FrontPort.objects.create(device=device, name='Front Port 1', type=PortTypeChoices.TYPE_8P8C)
+        rear_port = RearPort.objects.create(device=device, name='Rear Port 1', type=PortTypeChoices.TYPE_8P8C)
+        port_mapping = PortMapping.objects.create(device=device, front_port=front_port, rear_port=rear_port)
+        Job.objects.create(
+            name='Job 4', object=port_mapping, status='completed', queue_name='default', job_id=uuid.uuid4()
+        )
+        Job.objects.create(name='Job 5', status='completed', queue_name='default', job_id=uuid.uuid4())
+
+        response = self.client.get(reverse('core-api:job-list'), **self.header)
+
+        self.assertHttpStatus(response, status.HTTP_200_OK)
+        objects = {job['name']: job['object'] for job in response.data['results']}
+        self.assertIsNone(objects['Job 4'])
+        self.assertIsNone(objects['Job 5'])
+        self.assertEqual(objects['Job 1']['name'], 'Data Source 1')
+
 
 class BackgroundTaskTestCase(RQQueueTestMixin, TestCase):
     user_permissions = ()

netbox/extras/api/serializers_/tags.py

@@ -1,15 +1,9 @@
-from functools import cached_property
-
-from drf_spectacular.utils import extend_schema_field
-from rest_framework import serializers
-
 from core.models import ObjectType
 from extras.models import Tag, TaggedItem
-from netbox.api.exceptions import SerializerNotFound
 from netbox.api.fields import ContentTypeField, RelatedObjectCountField
+from netbox.api.gfk_fields import GFKSerializerField
 from netbox.api.serializers import BaseModelSerializer, ChangeLogMessageSerializer, ValidatedModelSerializer
 from users.api.serializers_.mixins import OwnerMixin
-from utilities.api import get_serializer_for_model
 
 __all__ = (
     'TagSerializer',
@@ -41,8 +35,11 @@ class TaggedItemSerializer(BaseModelSerializer):
         source='content_type',
         read_only=True
     )
-    object = serializers.SerializerMethodField(
-        read_only=True
+    # A plugin model can support tags without a REST API serializer
+    object = GFKSerializerField(
+        source='content_object',
+        read_only=True,
+        allow_missing_serializer=True
     )
     tag = TagSerializer(
         nested=True,
@@ -55,22 +52,3 @@ class TaggedItemSerializer(BaseModelSerializer):
             'id', 'url', 'display', 'object_type', 'object_id', 'object', 'tag',
         ]
         brief_fields = ('id', 'url', 'display', 'object_type', 'object_id', 'object', 'tag')
-
-    @cached_property
-    def _object_serializers(self):
-        return {}
-
-    @extend_schema_field(serializers.JSONField())
-    def get_object(self, obj):
-        """
-        Serialize a nested representation of the tagged object.
-        """
-        try:
-            serializer_class = get_serializer_for_model(obj.content_object)
-        except SerializerNotFound:
-            return obj.object_repr
-        if serializer_class not in self._object_serializers:
-            self._object_serializers[serializer_class] = serializer_class(
-                nested=True, context={'request': self.context['request']}
-            )
-        return self._object_serializers[serializer_class].to_representation(obj.content_object)

netbox/extras/tests/test_api.py

@@ -8,7 +8,7 @@ from unittest.mock import MagicMock, PropertyMock, patch
 from django.contrib.contenttypes.models import ContentType
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.db import IntegrityError
-from django.test import override_settings
+from django.test import override_settings, tag
 from django.urls import reverse
 from django.utils.timezone import make_aware, now
 from rest_framework import status
@@ -17,7 +17,20 @@ from core.choices import JobNotificationChoices, ManagedFileRootPathChoices
 from core.events import *
 from core.models import AutoSyncRecord, DataFile, DataSource, Job, ObjectType
 from dcim.api.serializers import SiteSerializer
-from dcim.models import Device, DeviceRole, DeviceType, Location, Manufacturer, Rack, RackRole, Site
+from dcim.choices import PortTypeChoices
+from dcim.models import (
+    Device,
+    DeviceRole,
+    DeviceType,
+    FrontPort,
+    Location,
+    Manufacturer,
+    PortMapping,
+    Rack,
+    RackRole,
+    RearPort,
+    Site,
+)
 from extras.api.serializers import EventRuleSerializer
 from extras.choices import *
 from extras.models import *
@@ -28,7 +41,7 @@ from netbox.registry import registry
 from users.constants import TOKEN_PREFIX
 from users.models import Group, ObjectPermission, Token, User
 from utilities.tables import get_table_for_model
-from utilities.testing import APITestCase, APIViewTestCases, disable_warnings
+from utilities.testing import APITestCase, APIViewTestCases, create_test_device, disable_warnings
 
 
 class AppTestCase(APITestCase):
@@ -1348,6 +1361,24 @@ class TaggedItemTestCase(
             self.assertEqual('slug' in tagged_item['object'], tagged_item['object_type'] == 'dcim.site')
             self.assertNotIn('custom_fields', tagged_item['object'])
 
+    @tag('regression')  # Ref: #23310
+    def test_list_objects_without_serializer(self):
+        """A tagged item whose object has no REST API serializer lists a null object."""
+        self.add_permissions('extras.view_taggeditem')
+        device = create_test_device('Device 1')
+        front_port = FrontPort.objects.create(device=device, name='Front Port 1', type=PortTypeChoices.TYPE_8P8C)
+        rear_port = RearPort.objects.create(device=device, name='Rear Port 1', type=PortTypeChoices.TYPE_8P8C)
+        port_mapping = PortMapping.objects.create(device=device, front_port=front_port, rear_port=rear_port)
+        tagged_item = TaggedItem.objects.create(tag=Tag.objects.get(slug='tag-1'), content_object=port_mapping)
+
+        response = self.client.get(reverse('extras-api:taggeditem-list'), **self.header)
+
+        self.assertHttpStatus(response, status.HTTP_200_OK)
+        results = {item['id']: item for item in response.data['results']}
+        self.assertIsNone(results.pop(tagged_item.pk)['object'])
+        for item in results.values():
+            self.assertEqual(item['object']['id'], item['object_id'])
+
 
 # TODO: Standardize to APIViewTestCase (needs create & update tests)
 class ImageAttachmentTestCase(